Slow-release lubricant additives in oil filters are known. The additives in some of these filters are incorporated into thermoplastic polymers which slowly dissolve into the oil being processed. See, for example, U.S. Pat. No. 4,075,098.In others, the additives are incorporated into polymers which are oil-permeable at elevated engine temperatures. See, for example, U.S. Pat. No. 4,066,559.In still others, the additives are incorporated into particles which are oil-insoluble but oil-wettable. See, for example, U.S. Pat. No. 5,478,463.In still another approach, oil-soluble solid polymers capable of functioning as viscosity improvers are provided inside an oil filter, with or without additional additives being incorporated into the polymer. See, for example, U.S. Pat. No. 4,014,794.
Although these systems are capable of introducing lubricant additives into the oil being filtered, they typically require inert carriers for slow release of the additives into the oil. In others, complicated mechanical systems such as capsules, perforated sheets, baffles, specially-designed injectors and/or additional compartments are needed for achieving slow release. See, for example, U.S. Pat. No. 5,718,258.
Accordingly, it would be desirable to provide slow release lubricant additives which do not require inert carriers or complicated mechanical systems for achieving slow-release metering of the additives into a fluid such as an oil.